This invention concerns an injection valve for injecting fuel into the combustion chamber of an internal combustion engine.
Such an injection valve is assumed to be known, for example, from U.S. Pat. No. 5,832,899. The housing of the injection valve consists of a nozzle part with an injection opening and a nozzle holder, on which the nozzle part is attached with a threaded bush. A longitudinally movable guided nozzle needle is accommodated in a bore of the nozzle part. Clamped between the nozzle holder and the nozzle part is an insert, which delimits on one side a control chamber in which the nozzle needle is located with its rear end facing away from the injection holes. On the opposite side, the insert has a discharge outlet, which is connected to the control chamber via a central bore and a discharge throttle. The control chamber is connected via an intake throttle to a fuel channel, which conducts fuel under pressure toward a nozzle chamber located ahead of the injection holes. The fuel pressure acting on the back of the nozzle needle when the discharge opening is closed holds the nozzle needle with a valve closing spring on a valve seat in the nozzle part, so that no injection occurs. If the discharge opening controlled by the control valve is released, the fuel pressure in the control chamber drops, and the nozzle needle lifts from its valve seat due to the fuel under injection pressure acting on the front of the nozzle needle. A disadvantage of the illustrated injection valve is that a large dead volume is formed by the closing spring located in the control chamber, which acts on the back of the nozzle needle. The reaction of the injector to the switching signals, however, is dependent upon the size of the dead volume of the control chamber. If, for example, an injection is to be initiated, then the dead volume must first be released, for which a time period is necessary, which increases the reaction time of the injection start with respect to the control signal. Inversely, the dead volume also causes an extension of the reaction time when the injection valve is closed to conclude the injection. Long reaction times affect the accuracy of the injection and worsen the suitability of the injector for the pilot injection.
It is an object of the invention to specify a closing spring arrangement with a simple construction which, on the one hand, allows a compact design of the injection valve and, on the other hand, makes possible short reaction times to switching signals.
This object of the invention is attained in that the closing spring is provided on the periphery of the nozzle needle below the nozzle needle guide outside of the control chamber.
This arrangement of the closing spring allows a compact design of the injection valve without having to tolerate a complicated construction. In a preferred embodiment, the face of a guide sleeve serves as abutment for the closing spring on the side of the housing. The nozzle needle is advantageously configured with a surrounding groove, in which an inwardly resilient pre-tensioned ring is locked, on which the spring plate of the closing spring can be supported.
An exemplary embodiment of the invention is explained with reference to the drawings.